Noise is a feature of everyday life: sound from conversations and the environment overlap to give rise to complex auditory input. Selective attention is required for navigation and communication in such complex scenes, but the role of attention in the neural representation and processing of sound streams in working memory is debated. Specifically, current theories suggest that attention enhances the representation of sound streams of interest while suppressing unattended sounds. However, these latter sounds may be key to task- switching and may still impact task-related processing. The goal of this study is to address the disparate roles proposed for unattended sounds in auditory scene analysis using a novel paradigm in which the number of acoustic features defining each stream (stream distinctiveness) and the presence of target-cues in unattended streams are varied during a selective attention task. The central hypothesis of this proposal is that unattended sound streams are processed to a greater degree than current theories propose and compete for cognitive resources during selective listening. This hypothesis will be tested in two specific aims: (1) to characterize the impact of multiple acoustic features on the representation of task-irrelevant sounds in working memory, and (2) to assess the degree of processing of task-irrelevant sounds and the impact of this processing on behavior. For each aim, a novel paradigm designed to isolate the contributions of multiple features and task-oriented attention will be used and EEG and behavioral measures will be recorded using established protocols. Results from this study will provide insight into the representation of sounds in complex auditory environments, and in particular, how these representations are influenced by bottom-up (stream distinctiveness) and top-down (task- oriented attention) factors. The knowledge gained will thus be a powerful resource for future investigations into auditory processing in natural environments and the development of technology for evaluation and assistance for those with auditory processing disorders.